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Modern Pearl River Delta and Permian Huainan coalfield, China: a comparative sedimentary facies study

PENG SUPING' and ROMEO M. FLORES ~ 'Beijing Graduate School, China University of Mining and Technology, Beijing 100083, P.R.C. and -~U.S. Geological Survey, Denver, CO 80225, U.S.A.

Abstract--Sedimentary facies types of the Pleistocene deposits of the Modern Pearl River Delta in Guangdong Province, China and Permian Member D deposits in Huainan coalfield in Anhui Province are exemplified by depositional facies of anastomosing fluvial systems. In both study areas, sand/sandstone and mud/mudstone-dominated facies types formed in diverging and converging, coeval fluvial channels laterally juxtaposed with floodplains containing ponds, lakes, and topogenous mires. The mires accumulated thin to thick peat/coal deposits that vary in vertical and lateral distribution between the two study areas. This difference is probably due to attendant sedimentary processes that affected the floodplain environments. The ancestral floodplains of the Modem Pearl River Delta were reworked by combined fluvial and tidal and estuarine processes. In contrast, the floodplains of the Permian Member D were mainly influenced by freshwater fluvial processes. In addition, the thick, laterally extensive coal zones of the Permian Member D may have formed in topogenous mires that developed on abandoned courses of anastomosing fluvial systems. This is typified by Seam 13-1, which is a blanket-like body that thickens to as much as 8 m but also splits into thinner beds. This seam overlies deposits of diverging and converging, coeval fluvial channels of the Sandstone D3 and, associated overbank-floodplain deposits. The limited areal extent of lenticular Pleistocene peat deposits of the Modern Pearl River Delta is due to their primary accumulation in topogenous mires in the central floodplains that were restricted by contemporaneous anastomosing channels. Copyright © 1996 Elsevier Science Ltd

Key words--Pleistocene sedimentary facies, Huanian coalfield, China, Pleistocene peat deposits, anastomosing river systems, Pearl River

INTRODUCTION was performed on as much as a 64 m-thick interval of the Pleistocene deposits of the Modern Pearl River The geomorphic pattern of the Modern Pearl River Delta from more than 1200 boreholes and as much Delta in the Guangdong Province, China (Fig. 1) as an 80 m-thick interval of the Permian Member D resembles that of a anastomosing fluvial system as from more than 6800 boreholes. The comparative recognized by Schumm (1968). He indicated that the study of these stratigraphic intervals focused on anastomosing fluvial system is composed of diverging recognition of similarities of their framework and converging channels separated by wetlands lithofacies architecture as illustrated by a series of infilled by fine-grained sediments. The work of Smith two-dimensional cross-sections, which were used to and Smith (1980) in the Upper Columbia River and interpret the environments of deposition. Smith (1983) in the Saskatchewan River of Canada Results of this study show that the Pleistocene showed that peat-forming mires developed in the deposits of the Modern Pearl River Delta were partly wetlands separating the anastomosing channels. deposited in an ancestral anastomosing fluvial system These investigations have guided facies analyses and that is now buried below the present fluvial-domi- interpretations of depositional environments of nated upper delta plain. Sedimentary facies types of coal-bearing strata containing genetically similar this ancestral fluvial system grade vertically and deposits in the Albian Upper Manville of east-central laterally into those of an ancestral branching fluvial Alberta, Canada (Putnam and Oliver, 1980), Pale- system now buried below the present lower delta ocene Fort Union Formation and Eocene Wasatch plain. This study also demonstrates a geographic Formation in the Powder River Basin, Wyoming relationship between peat-forming wetlands and (Flores, 1983; Warwick and Flores, 1987; Warwick diverging and converging, coeval channels of the and Stanton, 1988), and Westphalian C in the ancestral anastomosing fluvial system, which were Campine Basin, Belgium (Dreesen et al., 1995). flooded to some extent by riverine and estuarine This study analyzes and compares the sedimentary sediments via the ancestral branching fluvial system. facies types in the Pleistocene strata of the Modern These sediments, particularly the fluvially-trans- Pearl River Delta in Guangdong Province with those ported sediments, contributed mud to low-lying or of the Permian Member D in the Huainan coalfield topogenous mires that accumulated thin to thick in Anhui Province, China (Fig. l). Facies analysis peat, carbonaceous mud, and muddy peat. Similar

159 转载中国科技论文在线 http://www.paper.edu.cn

160 Peng Suping and Romeo M. Flores

anastomosing fluvial channel deposits interbedded plain is tidally influenced with a tidal range averaging with muddy floodplain deposits and associated from 0.60 to 1.68 m, Tidal currents modify sediments carbonaceous shale and coal beds were recognized in in the lower delta plain and redistribute delta-front the Permian Member D strata. However, in these sands into elongate bars resulting in flaring areal strata, estuarine sediments were not observed; instead geometries and branching estuarine distributary freshwater influence dominated the coal-forming channels. mires. The Modern Pearl River upper delta plain is fluvially influenced with the anastomosing channels

MODERN PEARL RIVER DELTA exhibiting a low gradient that averages from 0.023 to 0.037 percent (Figs 4 and 5). The width to depth ratio The Modern Pearl River Delta, which covers an of the anastomosing fluvial channels is about 4:1. The area of about 8600 sq. km and includes Pleistocene depths of these anastomosing fluvial channels are deposits as thick as 64 m, is located south of shallower than measured from the ratio because the Guangzhou, the capital of Guangdong Province, thickness of the channel deposits reflects a "com- China (Fig. 2). The delta plain was formed by Late posite" of a continuous vertically aggradation by the Pleistocene deposits of the Xijiang, Beijiang, Dongji- stream. The fluvial influence is manifested by ang, Tanjiang, and Liuxihe Rivers that prograded aggradation of small (about 400-500 m wide) to large into the Lingding Sea (embayment). These Late (about 1600-1800 m wide) coeval anastomosing Pleistocene deposits (Fig. 3) accumulated in an channels (Fig. 4). The areal density of these incised paleovalley that was carved into undifferenti- anastomosing fluvial channels is about 0.8 km/sq. ated Paleozoic sedimentary, metamorphic, and kin. The low gradient and high base level of these igneous rocks. The Modern Pearl River Delta can be anastomosing fluvial channels and associated muddy areally divided into a lower delta plain drained by overbank-floodplain environments controlled their branching distributary channels and an upper delta straight to slightly sinuous (sinuosity is about 1.25; plain drained by fluvial channels that display an Schumm, 1977) characteristics. The overbank and anastomosing pattern but not necessarily contempo- floodplain environments (Fig. 4) and abandoned raneous (Fig. 1). The Modern Pearl River lower delta courses of the anastomosing fluvial system (Fig. 5)

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Fig. I. Index map of China showing locations of the Modern Pear[ River Delta and Huainan coalfield. 中国科技论文在线 http://www.paper.edu.cn

A comparative sedimentary facies study 161

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served as wetlands, which are presently cultivated by very thin (1 mm) crenulated mud (Fig. 7). In into fish ponds and rice paddies. Where not addition, the trough crossbeds are armored by a cultivated, peat accumulated in mires of the clayey unit at the base (Fig. 6). The sand facies is floodplains. basally erosional and internally multiscoured; each scour surface is marked by gravelly sand (Figs 6 and 7). Each multiscoured sand unit ranges in thickness Sedimentary facies types from a few to tens of meters and from a few hundred The sedimentary facies types of the Pleistocene to thousands of meters in width (as wide as the deposits beneath the fluvial-dominated upper delta present width of the Modern Pearl River Delta plain of the Modern Pearl River Delta may be anastomosing channels). The upper part of the sand grouped into upward-fining sand, and randomly facies consists of fine grained sand that exhibits ripple interbedded mud, silt, sand, and peat facies types. laminations, lenticular beds, root marks, and animal The upward-fining sand facies is about 30 m thick, burrows (Fig. 8). 10-25 km wide, and marked by an erosional base. The interbedded mud, silt, sand, and peat facies This facies type consists of medium to coarse grained type is dominated by more than 50% muddy sand and contains mainly large-scale trough cross- sediments. However, silt and silty sand become beds, which are about 90 cm wide and 34 cm in height abundant where they are juxtaposed with the sand (Fig. 6). Trough crossbeds are occasionally burrowed facies type. These sediments contain cross and ripple by Ophiomorpha-like trace fossils consisting of laminations, which are commonly destroyed by plant vertical tubes (about 2 cm diameter) with sides lined roots. Burrowed lenticular and flaser bedded units in 中国科技论文在线 http://www.paper.edu.cn

162 Peng Suping and Romeo M. Flores

siltstones are commonly bounded by burrowed mud. woody organic remains and deposits are as much as The silty sand is present in coarsening-upward 5 m thick and 8-25 km in lateral extent (see Figs 9 successions where far removed from the sand facies. and 10). Palynpmorphs in the peat are composed The mud ranges from light to dark gray depending on primarily of Glyptostrobus pensillis. the organic content. This sediment is massive, rooted, locally heavily burrowed, piebald (mottled), and contains calcareous concretions. Whole shells and Stratigraphic .facies variations shell fragments of Ostrea sp., Cyclotella sp., The vertical sedimentary facies profile of the Late Cyclotella striata, Cyclotella divisus, and Chenondi- Pleistocene deposits of the Modern Pearl River Delta acea sp. are common body fossils in the mud. Mud is shown in Fig. 3. The facies profile exhibits a 1-20 contains abundant organic remains that physically m thick succession of sand and mud-dominated facies resembles a "muck or sludge." The mud-dominated types. This succession of sedimentary facies is facies type is thicker and more laterally extensive than interrupted by peat deposits occurring either in the the sand facies type. Peat is composed mainly of mud-dominated facies or above the sand facies.

SEDIMENTARY ENVIRONMENT ~Z LITHOLOGIC DESCRIPTION O COLUMN FACIES SYSTEM ¢3 v-

YELLOW SILTY MUD, HORIZONTAL BEDDING, PLANT DEBRIS FLOODPLAIN ANASTOMOSlNG FLUVIAL SYSTEM GRAY FINE GRAINED SAND, TROUGH CROSS BEDDING, TREE STEM REMAINS CHANNEL FILL

DARK GRAY SILTY MUD, FLASER BEDDING, LENTICULAR TIDAL FLAT BEDDING, BORROWS, Ostrea sp, Chenondiacea sp BRANCHING

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BLACK SILTY MUD, HORIZONTAL BEDDING PLANT DEBRIS, INTERDISTRI" Ost[ea sp r C. divisus etc, BUTARY BAY INTERLAYERED BLACK MUD AND SAND WITH PEAT WETLAND, MIRE LIGHT GRAY PEBBLED COARSE-GRAINED SAND, LARGE SCALE TROUGH CROSS BEDDING, TREE STEM REMAINS, EROSIONAL BASE CHANNEL FILL ANASTOMOSING

FLUVIAL SYSTEM INTERLAYERED MUD AND SILT WITH PEAT LENS WETLAND, MIRE

PIEBALD MUD, CALCAREOUS CONCRETION, LIMONITE. FLOODPLAIN

LIGHT GRAY GRAY SAND WITH LAMINATED MUD, UPWARD-COARSENING, CROSS BEDDING, Ostrea sp CHANNEL FILL BRANCHING

DARK GRAY SILTY MUD, HORIZONTAL BEDDING, INTERDISTRI- FLUVIAL SYSTEM Ostrea sp., Cyclotella striata, C divisus etc BUTARY BAY

INTERLAYERED SILT /~ND MUD wITH PEAT WETLAND, MIRE LIGHT GRAY PEC~BLED COARSE-GRAINED SAND WITH ANASTOMOSING LENTICULAR PEAT, UPWARD FINING, TROUGH CROSS BEDDING, CHANNEL FILL FLUVIAL SYSTEM EROSIONAL BASE

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•~-- TROUGH CROSSBEDS ~ RIPPLE LAMINATIONS ~) ~ FOSSIL SHELLS HORIZONTAL LAMINATIONS /~ROOT MARKS [ PLANTSTEMS

Fig. 3. A generalized stratigraphic column of the Late Pleistocene deposits of the Pearl River Delta. Lithofacies descriptions and interpretation of sedimentary environments of these deposits are included. 中国科技论文在线 http://www.paper.edu.cn

A comparative sedimentary facies study 163

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Fig. 4. A photograph showing the geomorphological characteristics of the anastomosing channels, overbank, and floodplains; the latter are cultivated into fish ponds and rice paddies southwest of Housan City. Guangdong Province. Buildings and houses are built along the overbank-floodplain deposits of the anastomosing fluvial system.

Fig. 5. A photograph of an abandoned course of the anastomosiiag fluvial system southwest of Housan City, Guangdong Province. Note discontinuous channels and cultivated floodplains. 中国科技论文在线 http://www.paper.edu.cn

164 Peng Suping and Romeo M. Flores

Fig. 6. A photograph of the sand facies of tile anastomosing fluvial system of the Modern Pearl River Delta in Nanhai County showing trough crossbeds. Tile trough crossbed (T) is draped by a clayey unit (C) at the base. For scale, pen is 16 cm long.

Fig. 7. An outcrop photograph of the sand facies of the anastomosing fluvial system of the Modern Pearl River Delta in Nanhai County showing trough crossbeds (T) overlain by a burrowed zone (B). For scale, hammer is 34 cm long. 中国科技论文在线 http://www.paper.edu.cn

A comparative sedimentary facies study 165

Fig. 8. An outcrop photograph of the sand facies of the anastomosing fluvial system of the Pearl River Delta in Xiaolan (Fig. 2) showing ripple laminations (RL) overlain by burrowed lenticular-bedded (L), clayey sandstone. For scale, pen is 16 cm long.

The two-dimensional lithostratigraphic variations The sand facies is laterally juxtaposed with of the Pleistocene facies types of the Modern Pearl mud-dominated facies as thick as 25 m shown by the River Delta are best shown in Figs 9 and 10. Figure 9 Pleistocene deposits below the modern upper delta displays facies variations of the Pleistocene deposits plain (anastomosing fluvial system: Fig. 10). Thin (10 parallel to the present depositional dip of the upper m or less) mud-dominated facies intervals are (anastomosing fluvial system) and lower (branching arranged in a "checkerboard" pattern with the fluvial system) delta plains of the Modern laterally offset sand facies in the Pleistocene deposits Pearl River Delta. Figure 10 exhibits facies variations below the modern lower delta plain (branching fluvial of the Pleistocene deposits perpendicular to the system; Fig. 9). Peat deposits, which are lenticular present depositional dip of the Modern Pearl River shape (see Figs 9 and 10), are commonly associated upper delta plain (anastomosing pattern but not with the muddy sediments in both Pleistocene necessarily contemporaneous fluvial system). The deposits below the modern upper and lower delta sand facies type is characterized by thin to thick and plains (anastomosing and branching fluvial systems). narrow to wide geometries. The thick (10-20 m), However, organic-rich muck or sludge is abundant in narrow ( < 15 kin) sand facies is multistoried and the Pleistocene deposits below the modern lower delta coeval, and best formed in the Pleistocene deposits plain (branching fluvial system; Fig. 9), whereas peat below the modern upper delta plain (see Figs 9 and lenses are more common in the Pleistocene sand 10: anastomosing fluvial system). The thin (10 m), facies below the modern upper delta plain (anasto- wide (greater than 20 kin) sand facies type is mosing fluvial system: Fig. 9). Fossil shells of Ostrea multilateral and coeval, and best developed in the and (:vclotella more commonly occur in the Pleistocene deposits below the modern lower delta Pleistocene mud-dominated facies below the modern plain (see Fig. 9; branching fluvial system determined lower delta plain (branching fluvial system) than that from plan view). This geometrically variable sand below the modern upper delta plain (anastomosing facies displays a coeval architecture in the Pleistocene pattern but not necessarily contemporaneous fluvial deposits below the modern upper delta plain system; Figs 9 and 10). (anastomosing pattern but not necessarily contemporaneous fluvial system) and laterally offset Sedimentary ./2lcies h2terpretation architecture in Pleistocene deposits below the modern The Pleistocene sand facies type is interpreted as a lower delta plain (branching fluvial system; see channel sand based on the erosional basal contact. Fig. 9). This sand facies was deposited by narrow, coeval, 中国科技论文在线

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Fig. 9. A NW SE cross-sectionoF the Pleistocene deposits or the Modern Pearl River Delta across the anastomosingfluvial system (tipper delt:t plain) and branching fluvial system (lower dehu plain). Line of section along city and or town localities is shown in Fig. 2. 中国科技论文在线 http://www.paper.edu.cn

A comparative sedimentary facies study 167

SW ANASTOMOSING FLUVIAL SYSTEM NE

Fig. 10. A SW-NE cross-section of the Pleistocene deposits of the Modern Pearl River Delta across the anastomosing fluvial system (upper delta plain). Line of section along city and/or town localities is shown in Fig. 2.

anastomosing channels (ancestral upper delta plain) anastomosing channel sands of the ancestral upper and wide, coeval, branching channels (ancestral lower delta plain were deposited in a narrow, straight to delta plain) similar to those in the Modern Pearl slightly sinuous, confined, and vertically aggrading River Delta (Peng Suping, 1990a, 1994). That the fluvial system is indicated by their thick, multistorey

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Fig. 1I. Geological and structural map of the Huainan coalfield, which covers an area of more than 8000 sq. km. The coalfield is concealed by Quaternary and Recent sediments (Q-R). inset is a north-south cross-section through the coalfield. T = Triassic, P = Permian, C = Carboniferous, 0 = Ordovician C = Cambrian, and A and Z = Precambrian rocks. 中国科技论文在线 http://www.paper.edu.cn

168 Peng Suping and Romeo M. FIores

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Fig. 12. Map showing location of the mining and exploration areas in the Huainan coalfield. Shaded areas are major mining districts. Lines of cross-sections A-A" and B-B" are shown in Figs 16 and 17. Map is shown as an inset in Fig. 11.

architecture. The sand facies of the ancestral Low-lying or topogenous mires developed in these anastomosing channel system was formed by cut and floodplains and formed thin to thick peat of fill as indicated by multiscour characteristics of the Glyptostrobus pensillis. Where the peat was invaded sand bodies. The sand facies of the branching channel by flocculated mud due to fluvial and estuarine system of the ancestral lower delta plain was processes, muck or sludge is formed. This process is probably deposited in sinuous (see Figs 2, 4 and 5), more common in the ancestral branching fluvial laterally aggrading distributary channels as indicated system (lower delta plain), by their thin, multilateral architecture and The vertical alternation of the Pleistocene anasto- subordinate, contemporaneous mud-dominated fa- mosing and branching fluvial deposits shown in the cies type. The presence of a few animal burrows (e.g. facies profile suggests that delta-lobe switching was Ophiomorpha-like) in the upper part of the sand facies pronounced during the time of deposition. This of the ancestral anastomosing fluvial system suggests depositional process was influenced by subsidence an estuarine depositional environment (Kamola, due to autocompaction of sediments, tectonism, or 1984). Here, mud armors at the base of trough eustasy. One of the major processes associated with crossbeds may indicate tidal influence (Ginsburg, many deltas is repetitive development of subaerial 1975; Reineck and Singh, 1980). land areas formed by delta-lobe progradation into The mud-dominated facies of the Pleistocene subaqueous interdistributary bays (Fisk, 1955; deposits is interpreted to have formed in the Galloway, 1975). In the Pleistocene deposits of the overbank-floodplain environment. The rooted, sand- Modern Pearl River Delta, the sedimentary facies silt rich sediments juxtaposed with the channel sand cycle of the ancestral branching fluvial system and represent overbank deposits. The mud-dominated overlying facies cycle of the ancestral anastomosing facies formed far from the overbank in the floodplain. fluvial system were followed by successions of similar Thick floodplain mud in the ancestral anastomosing facies cycles (Fig. 3). This indicates that a complete fluvial system reflects vertical accretion, which deltaic cycle (consisting of branching and anastomos- confined narrow fluvial channels. That these flood- ing fluvial facies cycles) was succeeded by younger plains of the ancestral anastomosing fluvial system deltaic cycles probably deposited in delta-lobes that were encroached by a minor amount of brackish switched or avulsed into interdistributary areas water via the ancestral branching fluvial system is (Fig. 3) as influenced by subsidence due to indicated by the presence of rare fossil shells of Ostrea autocompaction of sediments, tectonism, or eustasy. sp. Heavy bioturbation of the floodplain mud Repeated delta-lobe switching followed by infilling suggests subaqueous deposition in ponds or lakes. and abandonment developed several times during Pedogenesis on the floodplains is indicated by piebald deposition of the Late Pleistocene deposits of the or mottled mud. The piebald mud represents a Modern Pearl River Delta (see Fig. 3). Delta-lobe paleosol that may have been developed during abandonment, a process common in modern deltas subaerial exposure and/or groundwater fluctuation. (Coleman, 1976), was probably succeeded by The presence of burrowed, lenticular and flaser beds brackish-water transgressions that reached into the bound by burrowed mud suggests tidal influence ancestral anastomosing fluvial system (Fig. 10; NE particularly in low-lying parts of the floodplain. end of the cross-section). These transgressions may be 中国科技论文在线

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Fig. 13. A generalized stratigraphiccolumn of the Permian Member D and underlying Member C (part) showing lithofacies descriptions, geophysicallogs, sedimentaryfacies, and depositionalenvironments. Seam 13-1 is the most economiccoal in the Huainancoalfield. Sandstones D~ and D 3 are the most widespread beds in the strata. MS = mudstone; C SH = carbonaceousshale; F SS = fine-grainedsandstone. 中国科技论文在线 http://www.paper.edu.cn

170 Peng Suping and Romeo M. Flores

Fig. 14. ('ore photographs of thc sandstone litcics of thc Permian Member D showing trough (l 3.5 6} and planar (4 and 7) crossbcds and ripple laminations (g). Rule scale is 5 cm long.

related to sea level rises during the Late Pleistocene covers an area of more than 8000 sq. km (Figs I and time. 11). The coalfield contains coal-bearing strata of the Carboniferous Taiyuan Fornmtion, Permian Shanxi HI.:AINAN COALFIELD Formation (Member A), and Permian Lower Shihezi Formation (Member B). and Upper Shihczi The Huainan coalfield is located northwest of Formation (Members C G). Member D of tile Upper Hcfei, the capital of Anhui Province, China, and Shihezi Formation is the study interval. These slrata 中国科技论文在线 http://www.paper.edu.cn

A comparative sedimentary facies study 171

and older rocks were folded into a series of synclines facies type includes an erosional-based, fine- to and anticlines (Fig. 11). The coal-bearing strata are medium-grained sandstone, which makes up as much mined in three major areas (Panji, Xin-Xie, and as 50% of the total rock volume. This sandstone Xieqiao) that included 12 coal mines. Coal was facies averages about 20 m in thickness and 500 m explored in eight adjacent areas, where more than in width. The sandstone facies is fining-up- 6000 boreholes were drilled (Fig. 12). ward, trough crossbedded (4-6 cm in height, Fig. 14) in the lower part and ripple laminated in the upper Sedimentar3J~tcies t)'pes o[ Permian Member D o/" the part (Fig. 14, core 8; Fig. 15A, core la, ld, 2b d). Upper Shihezi k~rmatiof~ Some tabular crossbeds, as much as 10 cm in height, The Permian Member D of the Upper Shihezi occur in the sandstone facies (Fig. 14, cores 4 and 7). Formation (Fig. 13) is as much as 80 m thick and Lag conglomerates, consisting of coal spars, iron- consists of two sedimentary facies types. The first stones, and mudstone fragments, mark both the basal

Fig. 15. Core photographs of the sandstone facies of the Permian Member D showing basal lag deposits (lb,c, 2a, 2d,e) and ripple laminations (la,d, 2~d). For scale, the width of the core box is 60 cm. 中国科技论文在线 http://www.paper.edu.cn

172 Peng Suping and Romeo M. Flores

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Fig. 16. A cross-section of the Permian Member I) and Member (' coal-bearing strata in the Panji mine area (see Fig. 12 l\)r location). Vertical lines represent drill holes.

erosional surface and multiple internal scour surfaces (5- 10 m in thickness and 5 10 km in lateral extent). of the sandstone facies (Fig. 15, cores lb-.c: 2a, 2d-e). The framework architecture of the sandstone facies The second facies type consists of interbedded (Sandstones D2 and D~ in Figs 16 and 17) is coeval mudstone, siltstone, and silty sandstone; the mud- and laterally offset. Areal distribution of the stone is the most abundant rock type. This sandstone facies (Sandstones D, and D,, Fig. 13) is mudstone-dominated facies type makes up as much shown in Figs 18 and 19. An isopach map of as 50% of the rock volume of the Permian Member Sandstone D2 (Fig. 13) shows variations from < 10 D. The mudstone is gray to dark gray, massive, to > 20 m in thickness and indicates a sinuous, rooted, burrowed, and varicolored piebald (mottled; diverging, converging, and coeval areal distribution white and black blotches). It contains abundant (Fig. 18). The isopach map of Sandstone D~ (Fig. 13) siderite concretions and subordinate horizontal displays thickness variations from < 5 to > 15 m laminations or beds marked by finely macerated plant and suggests sinuous and coeval areal distribution fragments. Geochemical analysis of the mudstone (Fig. 19). However, Sandstone D, exhibits a higher indicates that the trace element boron is less than 50 density of sandstone facies types per squaI:e kilometer ppm and the Ca/Fe + Ca ratio is less than Sandstone D~. than 0.5, suggesting a freshwater origin (Garrels and The mudstone-dominated facies type is laterally Mackenzie, 1971). The mudstone is interbedded with juxtaposed to and encloses the sandstone facies type subordinate siltstone and silty sandstone which (see Figs 16 and 17). This facies type occurs within exhibit cross and ripple laminations. The mudstone is zones of nested sandstone facies and includes also interbedded with coal beds that range from 2 to interbedded coal, carbonaceous shale, and piebald 8 m in thickness and greater than 30 km in lateral mudstone beds (Peng Suping, 1990a). The latter rock extent (in cross-sections in Figs 16 and 17). The coal units comprise coal zones consisting of thin to thick beds are commonly interbedded with and grade beds, well displayed in the upper part of the Perlnian laterally into carbonaceous shale beds. Member D. These coal zones, which are separated by sandstone and mudstone-dominated facies types, Stratiqraphic ./hcies variations may be interpreted as cyclical or repetitive zones. The vertical facies profile of the Permian Member Some coal and carbonaceous shale beds are also D (Fig. 13) indicates a dominant thick sandstone sparsely distributed in the facies types between these facies in the lower part and mudstone-facies in the coal zones (Figs 16 and 17). The coal zone of the upper part. The thick sandstone facies overlies the Permian Member D in tandem with the coal zone or thin coal beds of the Permian Member C. Thin to coaly unit of the underlying Permian Member C are thick coal beds are common in the upper part separated by a 30-60 m thick interval. These coal (including Seam 13-1) and generally interbedded with zones may be interpreted as cyclical or repetitive siltstone, mudstone, and thin coarsening- and zones. Coal and carbonaceous shale beds are also lining-upward silty sandstone beds. sparsely distributed between these coal zones (Figs 16 Cross-sections (Figs 16 and 17) show the and 17). The coal zones represent the most persistent stratigraphic variations of the facies types of the component of the mudstone-dominated facies type Permian Member D. The lowermost coaly unit is occurring for over 30 km distance. included in the uppermost part of the Permian The coal zones contain coal beds as much as 8 m Member C. Thus, the boundary between the Permian thick (e.g. Seam 13-1, Figs 13, 16, and 17), which Member C and Member D is a vertically gradational laterally split into thinner beds. The coal beds and laterally interfingering contact above the are split by sandstone and mudstone-dominated uppermost coal zone of the Member C (see Figs 16 facies types. The coal-bed splits, in turn pinch out and 17). The sandstone facies of the Permian Member or shale out. Seam 13-1 is >4 m thick in the Panji D varies in geometry from lenticular (10-30 m in No. 1 mine, Xinji-Guiji area, and Kongji-Xie thickness and 1-5 km in lateral extent) to elongate No. 3 mine area (Fig. 20). Another area of thick 中国科技论文在线

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A comparative sedimentary facies study 177

seams occurs in Xieqiao-Hanzang. Seam 13-1 broad courses of the anastomosing fluvial system, are generally thins less than 3 m to the north, east, and more laterally persistent than those described by west of these areas, although local thickening occurs Smith (1983) and Smith et al. (1989). Seam 13-1 along the Guandianji-Panji belt (Fig. 20). When represents coal accumulation in mires developed on these areas of local thickening and thinning are abandoned courses of the anastomosing fluvial combined, Seam 13-1 is about 6--35 km wide and system that deposited Sandstone D3 as indicated by > 56 km long, with a blanket-like body. the stratigraphic vertical juxtaposition of these deposits. That these mires were low-lying or topogenous is indicated by splitting of the coal Sedimentary facies interpretation beds by floodplain sediments (e.g. Seam 13-1; Figs 16 The sandstone facies type of the Permian Member and 17). Repetitive accumulations of these clastic- D is interpreted as a fluvial channel sandstone as and organic-rich intervals may have been controlled evidenced by an erosional base below the sandstone by subsidence due to local differ- bodies. The internal multiscoured characteristics of ential autocompaction of the sediments or basin the sandstone facies type suggest deposition by cut subsidence or combination of both, accompanied by and fill fluvial processes. The sandstone facies, as autocyclic processes of the fluvial depositional typified by the Sandstones D2 and D3, displays a system. coeval, diverging, and converging areal distribution suggesting deposition in an anastomosing fluvial COMPARISON AND DISCUSSION system. The elongated (thin and lengthened) sandstone facies may indicate lateral aggradation of the A comparison of the sedimentary facies types fluvial channels in contrast to the lenticular (thick and depositional environments of the Pleistocene and lens shaped) sandstone facies, which suggests deposits of the Modern Pearl River Delta and vertical aggradation of the fluvial channels. The Permian Member D deposits indicates some simi- occurrence of these sandstone facies types as larities in~ (1) channel sand/sandstone and overbank- contemporaneous units, which is indicated in Figs 18 floodplain facies, (2) areal anastomosing pattern of and 19, suggests that both vertical and the channel sand/sandstone facies, (3) deposition of lateral aggradation simultaneously developed in the the channel sand/sandstone facies in vertically and alluvial plain. These processes are typical in laterally aggrading fluvial systems, (4) overbank- anastomosing fluvial systems described by Smith and floodplain facies, which consist of abundant Smith (1980), Smith and Putnam (1980), Flores mudstone and subordinate siltstone and silty (1983), Flores and Hanley (1984), Smith (1983), sandstone, (5) peat/coal facies, which are formed in Warwick (1985), Smith et al. (1989), and Flores low-lying or topogenous mires in the mud-dominated and Cross (1991). Peng Suping (1986), Lan Changyi overbank-floodplain environment, (6) floodplain et al. (1988), Peng Suping (1990b) and Peng Suping environment that contains ponds or lakes, (7) et al. (1991) suggested that deposition of the Permian subaerial condition and/or groundwater fluctu- Member D occurred in an anastomosing fluvial ation, which reflect seasonal climate and paleosol system. development, and (8) cyclical deposition of the The mud-dominated facies of the Permian Member fluvial sediments as influenced by autocyclic pro- D is interpreted as overbank-floodplain deposits. The cesses due to autocompaction and/or tectonic siltstone and silty sandstone interbeds of the subsidence. mudstone-dominated facies represent sediments de- Differences between the sedimentary facies types posited in the levee-overbank and floodplain environ- and depositional environments of the Pleistocene ments during floods. That the floodplain environment deposits of the Modern Pearl River Delta and was subaqueous, thus forming ponds or lakes, is Permian Member D deposits include: (I) brackish indicated by bioturbation of the sediments. However, water influence as evidenced by oyster shells for the subaerial conditions and/or groundwater fluctuation ancestral anastomosing fluvial system of the Modern in the floodplains are indicated by the formation of Pearl River Delta, (2) mainly freshwater influence as piebald or mottled mudstone, which may be a evidenced by megaflora in the fluvial environments product of pedogenesis (paleosol). Groundwater for the Permian Member D, (3) deposition of the fluctuation reflects a seasonal climatic (wet vs dry) ancestral fluvial systems of the Modern Pearl River condition (Thorez et al., 1994). The coal, which Delta complex in an incised paleovalley, (4) fluvial contains carbonaceous shale and piebald mudstone, deposition of the Permian Member D as a part of an reflects deposition in low lying or topogenous mires alluvial plain in a subsiding basin, (5) minor peat and floodplains, which were occasionally interrupted accumulation in small low-lying or topogenous mires by fluvial processes. These beds, which occur as between ancestral anastomosing channels of the persistent coal zones that separate intervals of nested Modern Pearl River Delta, and (6) coal zones formed sandstone and mudstone-dominated facies types, in extensive low-lying or topogenous mires developed indicate that they were accumulated in extensive in abandoned courses of anastomosing fluvial mires. These mires, usually formed in abandoned systems. 中国科技论文在线 http://www.paper.edu.cn

178 Peng Suping and Romeo M. Flares

CONCLUSIONS Flares R. M. and Hanley J. H. (1984) Anastomosed and associated coal-bearing fluvial deposits: Upper Tongue Although the sedimentary facies types and areal River Member, Paleocene Fort Union Formation, geomorphology of the Pleistocene anastomosing northern Powder River Basin, Wyoming, U.S.A. In Sedimentology of Coal and Coal-bearing Sequences fluvial channels and associated overbank-floodplains (Edited by Rahmani R. A. and Flares R. M.), pp. 85-103. developed beneath the Modern Pearl River upper Inter. Assoc. of Sediment. Spec. Publ. No. 7. delta plain appear to be identical to those determined Galloway W. E. (1975) Process framework for describing for the Permian Member D, we can not categorically the morphologic and stratigraphic evolution of deltaic suggest a complete resemblance in their depositional depositional systems. In Deltas (Edited by Broussard M. L,), p. 87098. Houston Geol. Sac. systems. The freshwater influence in the Permian Garrels R. M. and Mackenzie F. T. (1971) Evolution of Member D deposits indicates that the anastomosing Sedimentary Rocks. W. W. Norton and Co., New York, fluvial channels were accumulated in an alluvial 397 pp. plain. This freshwater setting probably contributed to Ginsburg R. N. (1975) Tidal Deposits: A Casebook of Recent Examples and Fossil Counterparts. Springer, New York, accumulation of thick and extensive coal deposits in 428 pp. floodplain topogenous mires, which were probably Kamola D. L. (1984) Trace fossils from marginal marine protected from detrital influx. This setting is in facies of the Spring Canyon Member, Blackhawk contrast to the influence of tidal-estuarine and Formation (Upper Cretaceous), east-central Utah. brackish-water processes on topogenous mires in the J. Paleont. 58, 529-541. Changyi Lang, Bencai Yang and Suping Peng (1988) Pleistocene anastomosing fluvial system of the Depositional environment and coal accumulation of Modern Pearl River Delta, in which only sparse, Permian coal bearing strata, Huainan coalfield. J. China thick peat deposits accumulated. Coal Sac. 13, I 1-22. Suping Peng (1986) The coal-forming model of the Acknowledgements--This study was funded by the China anastomosed channel system of Permian Member D, Natural Science Foundation under the grant Project No. Huainan coalfield, China. 12th Inter. Sediment. Congress 8900017. This paper was prepared while Peng Suping was Abs., Canberra, Australia, p. 328. a (June-August 1994) visiting scientist under the supervision Suping Peng (1990a) Fundamental characteristics of the of R. M. Flores at the U.S. Geological Survey in Denver, anastomosing fluvial system on complex delta plain. Colorado. Fieldwork for the senior author in Tertiary Chinese Sci. Bull. 35, 835-839. Rocky Mountains coal-basin analogues for the China study Suping Peng (1990b) Characteristics and origin of piebald was supported by the USGS Human Resources Initiative mudstone in Permian member D in Huainan coalfield. Volunteer Funding. The senior author extends appreciation Geol. Rev. 36, 326-332. of assistance to the China Academy of Science, the Suping Peng (1994) Depositional model and characteristics Chairman of Sedimentological Society of China, Professor of a complex delta. J. China Coal Sac. 19, 89-98. Ye Lianjun, the President of the China Laboratory of Coal Suping Peng, Dexin Han, Pengfei Zhang and Changyi Lan Geology, Professor Han Dexin, and Professor Zhang (1991) Paleodrainage characteristics of Permian Members Pengfei. Appreciation is extended to Frank G, Ethridge of C and D, Huainan coalfield. Sinica Sedimenta. Acta 9, Colorado State University, and Ronald W. Stanton and 1-10. Peter D. Warwick of the U.S. Geological Survey for Putnam P. E. and Oliver T. A. (1980) Stratigraphic traps in editorial suggestions, helpful comments, and improvements channel sandstones in the Upper Manville (Albian) of to the paper. east-central Alberta. Can. Petrol. Geol. Bull. 28, 489-508. Reineck H.-E. and Singh I. B. (1980) Depositional Sedimentary Environments with References to Terrigenous REFERENCES Clastics. Springer-Verlag, New York, 549 pp. Schumm S. A. (1968) Speculations concerning paleohydro- Coleman J. M. (1976) Deltas: Processes of Deposition and logic controls on terrestrial sedimentation. Geol. Soc. Am. Models of Exploration. Continuing Educ. PuN. Co., Inc., Bull. 79, 1573 1588. Champaign, Illinois, 102 pp. Schumm S. A. (1977) The Fluvial System. John Wiley and Dreesen R., Bossiroy D., Dusar M., Flares R. M. and Sons, New York, 338 pp. Verkaeren (1995) Overview of the influence of syn- Smith D. G. (1983) Anastomosed fluvial deposits: modern sedimentary tectonics and palaeo-fluvial systems on coal examples from Western Canada. In Modern and Ancient seam and sand body characteristics in the Westphalian C Fluvial Systems (Edited by Collinson J. D. and Lewin J.), strata, Campine Basin, Belgium. In European Coal pp. 155-168. Inter. Assoc. of Sediment. Spec. Publ. 6. Geology (Edited by Whateley M. K. G. and Spears D. D.), Smith D. G. and Putnam P. E. (1980) Sedimentation in pp. 215-232. Geol. Sac. Spec. Publ. No. 82. anastomosed river systems--modern and ancient Fisk H. N. (1955) Sand facies of Recent Mississippi delta examples in Alberta, Canada. Can. J. Earth Sci. 17, deposits. 4th World Petrol. Congress Proc., Rome, 1396-1406. Secular 1, 377-398. Smith D. G. and Smith N. D. (1980) Sedimentation in Flares R. M. (1983) Basin facies analysis of coal-rich anastomosed river systems: Examples from alluvial Tertiary fluvial deposits, northern Powder River Basin, valleys near Banff, Alberta. J. Sediment. Petrol. 50, Montana and Wyoming. In Modern and Ancient Fluvial 157-164. Systems (Edited by Collinson J. D. and Lewin J.), Smith N. D., Cross T. A., Difficy J. P. and Clough S. R. pp. 501-515. Inter. Assoc. of Sediment. Spec. Publ. (1989) Anatomy of an avulsion. Sediment 36, 1-23. No. 6. Thorez J., Flores R. M. and Caudron M. (1994) Clay Flares R. M. and Cross T. A. (1991) Cretaceous and geology, micromorphology, and geochemistry of an Tertiary coals of the Rocky Mountains and Great Plains Eocene paleosol in the Willwood Formation, southern regions. In Economic Geology, U.S.: The Geology of Bighorn Basin, Wyoming: an overview. In Organics and North America (Edited by Gluskoter H. J., Rice D. D. and the Rockies Field Guide (Edited by Flores R. M., Mehring Taylor R. B.), pp. 547-571. Geol. Sac. of Amer., Boulder, K. T., Jones R, W. and Beck T. L.), pp. 139-148. Wyo. Colorado. State Geol. Surv., Public Information Circular No. 33. 中国科技论文在线 http://www.paper.edu.cn

A comparative sedimentary facies study 179

Warwick P. D. (1985) Depositional environments and Sedimentology (Edited by Ethridge F. G., Flores R. M. petrology of the Felix coal interval (Eocene), Powder and Harvey M. D.), pp. 303-310. Soc. of Eco. Paleont. River Basin, Wyoming. Unpublished Ph.D. Thesis, and Mineral. Spec. Publ. No. 39. University of Kentucky, Lexington, 333 pp. Warwick P. D. and Stanton R. W. (1988) Depositional Warwick P. D. and Flores R. M. (1987) Evolution of fluvial models for two coal-bearing sequences in the Powder styles in the Eocene Wasatch Formation in the Powder River Basin, Wyoming, U.S.A.J. Geol. Soc. London 145, River Basin, Wyoming, In Recent Developments in Fluvial 613-620.